1. Field of the Invention
The present invention relates to an IC tester for testing a semiconductor integrated circuit, particularly relates to an IC tester which decides output values of devices under test and tests function and electric characteristics of the semiconductor integrated circuit.
2. Description of the Related Art
A variety of electronic devices have been recently quickly developed in an IC (Integrated Circuit). An IC, an LSI (Large Scale Integrated circuit), etc. realize the operations of respective elements such as a resistor, a capacitor, a transistor, by circuits which are formed by a printing method, evaporating method, etc. However, there occur slight variations in respective device characteristics between mass-produced devices. An IC tester tests whether the characteristics of the IC or LSI meet the standard or not.
In testing an IC by an IC tester, a pattern signal necessary for testing respective devices under test is inputted to given device pins of the device under test, and an output signal of the device under test relative to the pattern signal is decided by a decision circuit to decide the result of test. At that time, a comparator is connected to an output pin of the device under test as shown in FIG. 6(A), wherein a reference voltage is compared with an output voltage of the device under test by the comparator, so that the output of the comparator is rendered high signal if the output voltage is higher than the reference voltage, and it is rendered a low signal if the output voltage is lower than the reference voltage as shown in FIG. 6(B).
Further, as shown in FIG. 7, the decision circuit decides the result of test of the device under test by the conditions of output signals of the comparator at the timings of decision trigger signals respectively outputted from the timing generating circuit.
However, there are following problems in the conventional IC tester having the construction set forth above.
1. In the conventional comparator, since there is only one comparator relative to one output, and there is only one reference voltage, the comparison whether the voltage value of the output signal of each device under test is high signal or low signal is performed, so that the decision of the result of test by the decision circuit is performed in two manners, i.e., pass or failure of test of the device under test.
2. In the conventional decision circuit, only the decision of the result of test of each device under test has been conventionally performed only at one point along the time axis at the timings when the decision trigger signals are inputted, the decision of the condition of the device under test can not be performed in a period of time other than the aforementioned period of time.